1. Field of the Invention
This invention in general relates to a prime mover based upon a centrifugal reverse flow disk turbine, which is applicable to steam, gas, water, and air turbines, and a method to yield a rotational power thereby.
2. Related Art
In conventional turbines, which have been operated in fossil and nuclear power plants, for example, large-scale steam (water) turbines more than one gigawatt (GW) under a supercritical condition are utilized in order to minimize the steam rate and to improve the thermal efficiency thereof.
However, it is estimated that these fossil and nuclear fuels on the earth would run out at end of this century as clearly projected in FIG. 11. FIG. 11 includes all kind of energy resources on the earth, i.e. fossil fuels (oil, coal, and natural gas), and nuclear fuel, as well as methane hydrate therewith.
Another crucial issue human beings are now facing with is global warming due to carbon dioxide (CO2) emissions into earth's thin planetary boundary layer, mainly caused by combustion of fossil fuels as mentioned above. The British government's chief scientific adviser, Sir David King, has described global warming as a greater threat than terrorism. (The Japan Times, Feb. 4, 2005)
According to a recent super-computer projection (Saitoh and Wakashima, Green Life, Mar. 2006), as indicated in FIG. 10, the CO2 concentration in the atmosphere will increase to 1250 ppmv within 100˜200 years as in FIG. 12. What is the most outstanding feature of our simulations is that after taking a maximum, the CO2 concentration will stay almost constant during 50000 years thereafter.
While, urban environment in mega-cities like Tokyo is still getting worse and worse. For example, the concentration of NO2 is still increasing and above a regulated level in the Tokyo metropolitan area. The cause of aggravation of the urban environment can be mainly attributed to increase of automobiles in the urban area. This serious environmental issue is called “urban warming (or heat island)”, which is caused by a concentrated consumption of energy in the urban area.
These two major restrictions oblige human to change their life styles and use renewable energies including solar, wind, ocean, geothermal, and biomass, other than fossil fuels.
However, the renewable energy is dispersed and attainable temperature and pressure are sometimes low, thereby leading to a down-sized prime mover. This down-sizing brings conventional turbine a great aggravation of thermal efficiency illustrated clearly in FIG. 13.
Further, multi-staging and reheating/regenerating cycles, which have been very common in conventional large-steam turbines could not be exploited in a small turbine because of a strict cost limitation.
A typical conventional large-scale steam turbine is of axial flow one having three-dimensional static and moving blades mounted on the housing and the rotor, respectively. The working fluid (for ex. water steam), in general, flows axially, so that the physical properties of steam may considerably change on its way to the last stage, thereby bringing the rotor diameter variation.
This causes complicatedness and high cost of a entire system (about 100˜500 times higher than conventional gasoline engine and the same power rated engines). This fact greatly hinders market permeation of the small-sized turbines.
In above-mentioned large-scale steam turbines, a supercritical condition (a condition exceeding pressure: 22.12 MPa, and temperature: 375.15 degree Celsius for water vapor) was adopted to raise its thermal efficiency. Nonetheless, the thermal efficiency of even the latest most advanced fossil-powered steam turbine is at most 40˜42%, this value being only 60% of the ideal Carnot cycle efficiency.
If the conventional steam turbine were down-sized to 10 kW, say, the thermal efficiency would be reduced to only 3˜5%, which is by far less than average photovoltaic cell efficiency (about 10%; annual mean).
[Tesla's Pioneering Works on Bladeless Disk Turbine]
Nikola Tesla (1857-1943), who was a US electric engineer, known as an inventor of induction motor, alternating current, Tesla coil, and magnifying transmitter, etc., conducted an intensive work on his Tesla bladeless turbine during the period from 1908 to 1930. Examples of his invention are seen in many prior art patents, including U.S. Pat. No. 1,061,142 and U.S. Pat. No. 1,061,206.
In the disk turbine, which bears his name, the rotor is composed of a plurality of flat plates which are set in motion through the adhesive and viscous action of the working fluid, entering the system tangentially at the periphery and leaving it at the center. At that time, the Tesla's turbine was spotlighted as a thermodynamic transformer of an actively surprising by far that of any other prime mover theretofore.
Around 1910, Tesla built his 200 horsepower turbine with rotor diameter of 18 inches, which turned at a speed of 9000 revolutions per minute. This turbine was situated in the Waterside Station, the main powerhouse of the New York Edison Company.
However, at his time, the trend was rapidly changing toward another type of turbines; i.e. Parsons and Curtis turbines, these were well entrenched in the development stage. As the history shows, these axial flow turbines have swept over the world thereafter. Tesla was a late starter. Had Tesla advanced with the development of his turbine as early as 1889 when he returned from the Westinghouse plant, the Tesla turbine might perhaps have been completed. This was really a turning point for the Tesla turbine.
However, mankind is now facing an unprecedented environmental age; namely, global warming due to CO2 emissions, urban warming due to heat emissions in city area, exhaustion of fossil and nuclear fuels, problems of population growth, food production, drinking water scarcity, and other resources. In order to resolve all crucial issues stated above, exploitation of renewable energies such as solar, wind, geothermal, ocean thermal, biomass, various kinds of temperature differences etc. is inevitable and some of those have been partly introduced in the market. A Green New Deal Plan also comes up with by the Obama cabinet, last year.
With a tailwind of time and recent advancement of materials, and cutting-edge manufacturing technology, and computer simulation technique, as well as numerical methods involved, a sophisticated and highly-advanced version of Tesla turbine is brought back to life in a long absence of 100 years. In this sense, Tesla was a prodigal genius who dreamed and projected the future.
Advanced technologies such as multi-staging and reheating/regenerating cycles, which have been very common in conventional large-steam turbines, could not be exploited anymore in a small turbine because of a strict cost limitation. Instead, the present invention based on Tesla turbine having the great advantages of i) simplicity of design, ii) low noise and vibration level, iii) stability in operation, easy maintenance, iv) economies of construction, and lastly, v) very high-efficiency will reign over the world in the 21st century.
It is especially noted here that without Tesla's pathfinding and profound original works, the present invention could not be accomplished at all.
As an important measure for evaluating all kinds on prime movers which will appear in the 21st century, the most appropriate one will be the Carnot efficiency ratio (abbreviated as CER thereafter), this being a ratio of the real prime mover (engine) against the Carnot efficiency, that implies a maximum attainable limit among all kinds of prime movers ever appeared in the history or will appear in the future.
The Carnot efficiency ratios for typical engines and prime movers are illustratively plotted in FIG. 13, including Gasoline engine (TOYOTA Prius), Diesel engine, Gas turbine, Steam turbine, Scroll engine, Gas engine, Vane-type engine, Stirling engine, and recent Fuel cell. It is again noted that the thermal efficiency is about twice better than conventional gasoline engine (see Prius in FIG. 13).
[Prius]
Since the great invention of gasoline-powered vehicle by Gottlieb Daimler and Karl Benz, almost simultaneously, in 1886, the gasoline engines have been widely accepted and swept over the whole world more than a century. Further, those engines are still dominating the world.
Although its reliability and cost effectiveness are overwhelming, efforts toward an improvement of the thermal efficiency of the gasoline engine is strictly limited owing to an old cycle of the engine, i.e. the Otto cycle. This engine could not survive any more in the environment-compatible 21st century.
Evaluating the Prius (first manufactured in 1997 by TOYOTA) which has the best thermal efficiency (as a gasoline engine vehicle) in the world, one can judge whether the Prius would be earth-compatible or not. For example, the Carnot efficiency ratio (CER) of the Prius is only 0.44, thereby indicating a low compatibility against the environment.
Spencer Abraham, who was the Administrator of Energy Agency of Clinton Cabinet, estimated that the number of cars in 2050 would be 3.5 Billions. If this projection were true, and the business would go as usual, the energy consumption by cars would amount to about 9 TW (terawatts), this being more than a half of the current consumptions.
The Prius can curtail the fuel consumption to a half, however, this is not sufficient to mitigate global warming at all, since the energy consumption by cars will exceeds 16 TW even if all vehicles were replaced with the hybrids equivalent with the Prius.
[Fuel Cell]
As a next generation prime mover, fuel cell has been spotlighted and many automobile manufacturers placed much attention upon this promising future technology.
However, the fuel cell has three major crucial problems, which can not be solved easily; one is the energy resource. The fuel cell uses gaseous hydrogen, but hydrogen does not exist in nature as it is. It must be reformed from existing fossil fuels or by virtue of electrolysis from water by utilizing electricity via e.g. photovoltaic cell which is a carbon-free energy source. However, total transforming efficiency of solar to hydrogen route is very low, say, 3˜5% at maximum.
Secondly, the energy transforming efficiency of the fuel cell is relatively low; a theoretical efficiency reaches over 50%, but the auxiliary power needs at least 7% of generated electricity, thereby reducing the net power from the fuel cell. Current efficiency is around 40%, which is almost equal to the Prius' efficiency.
Lastly, life expectancy and cost itself; since the fuel cell involves a chemical reaction process, degradation such as membrane is inevitable, thereby reducing its life expectancy. Also considered as another crucial barrier is its cost.
It will take a long time period (more than 30˜50 years) to resolve three problems mentioned above.
[Stirling Engine]
Stirling engine, invented in 1816 by Robert Stirling who was a Scotland engineer, was once regarded as a promising prime mover in 1980's. In early times of development, the Stirling engine was considered to work at a low temperature difference, which is appropriate for solar applications.
However, at present, the Stirling engine can operate efficiently only for a high-temperature range above 700˜800 degree Celsius. Further, its thermal efficiency is not sufficient.
[FORD Organic Rankine Cycle Turbine]
From 1976 to 1984, a Solar Thermal Power System Project was conducted by the Jet Propulsion Laboratory (JPL). Ford Aerospace and Communications Corporation designed and assembled the organic Rankine cycle turbine, which was the first tentative Rankine cycle and a pioneering work toward an epoch-making prime mover (Leonard D. Jaffe, J. of Solar Energy Engineering, Vol. 110, November 1988, pp. 275-281). As an expander, a radial turbine of single stage impulse type was adopted and toluene was used for the working fluid to cover a high temperature range.
Although the turbine adopted was the conventional radial turbine, they obtained the maximum conversion efficiency of 23 percent and the output power of 21.6 kW with the Carnot efficiency ratio being 44 percent.
This project was indeed very valuable one since it was done as early as 1970's and the validity of organic Rankine cycle was first recognized. If the present invention were incorporated in that project, the vehicle mileage would be at least twice better than the Prius; i.e. 89.4 mpg (or 76 km/l).
[Photovoltaic Cell]
Photovoltaic cell (PV) was first introduced as early as 1950's in US Space program. It has over 50 years history, but the generation efficiency for electricity is still as low as only 10 percent on yearly averaged base. PV is promising technology among solar electricity generation devices. However, there are some barrier in dissemination of PV systems. One is relatively low efficiency and another high cost.
Moreover, the PV can not be used as a bottoming cycle and it needs a battery for energy storage, thereby restricting vulnerability.
[NASA Micro-Gas Turbine]
A micro-gas turbine for use in space was developed by NASA, schematically shown in FIG. 14. The turbine includes solar receiver, waste heat radiator, regenerator (heat exchanger), compressor, generator, and turbine expander. The output power is 10 kW at 36000 rpm, under inlet temperature of 1144K. According to NASA, its thermal efficiency is reported to be 29%, which indicates that the CER(Carnot efficiency ratio) is only 0.39.
[Previous Off-Centered Design Disk Turbine]
A disk turbine with reverse direction channel flow, which is different from the present invention, is described in Japanese patent application laid-open disclosure number 2004-278335 and 2005-188378. A typical experimental result was designated in FIG. 15, showing output power versus speed of rotation. It is quite noteworthy that a stall phenomenon clearly appears after taking its maximum power around 3500 rpm. An abrupt decrease of power is seen, thereby causing a dead output at early rotational speed of 5000 rpm as indicated in FIG. 15. This stall phenomenon is of crucial importance since the thermal efficiency is restricted thereby.
Power due to the viscous force in the above case is proportional to 2.5 power to angular velocity of rotation (ω), so that viscous power loss increases abruptly with rotational speed.
This fatal disadvantage was brought about owing to off-centered design concept itself. Further, there existed a Joule-Thomson effect, which appears in tip clearance region between the housing and the rotor tip.
[Steam Turbine in Power Plants]
FIG. 16 shows the relation between a power rating and a specific steam rate for a steam turbine in power plants, etc., wherein an ordinate indicates the steam rate (kg/h) for generating a power of 1 kW. In this graph, it is seen that the higher the performance of the steam turbine becomes, the lower the steam rate, and this implies the reason why the steam rate in a giant power plant such as a power rate of 1,000,000 kW is low. On the other hand, it is understood in the graph that the efficiency becomes worse in a micro steam turbine of 1 to 100 kW by one tenth.
It is considered that this is resulted from the fact that a flow through (useless flow; not contributing to the power) which flows through tip clearances around a periphery of a rotor, blades, and so on becomes large. In addition, heat transfer and friction loss at wall per unit flow rate are increased to extremely lower an efficiency, together with a surface area per unit flow is large.